What does the age have something to do with this? Its a genuine shower thought, nothing related to age.

I think the implied meaning is that it’s a very clever question and it’s unexpected for someone so young to think of it. So it’s kind of a humblebrag that their daughter is smart.

She could definitely be smart and likely isn’t dumb, but I don’t think this level of thinking is out of the ordinary for a 12 year old.